32 BULLETIN 1121, U. S. DEPARTMENT OF AGRICULTURE. 
it seems difficult to believe that the superioity of the crossbreds is due 
merely to dominance of factors present in some of the inbred families, 
but absent in others, the hypothesis which will be at the basis of our 
later discussion. We are, however, able to analyze the character 
which we are considering into four components. The crossbreds do 
not exceed the best inbred family to anything like as great an extent 
in each of these component characters. The superiority of the cross- 
breds is consistent, however, and hence cumulative, in comparison with 
the superiority of the best inbred family over the average, the ‘‘ best”’ 
inbred family being one family in one case and another in another. 
The four component characters are themselves doubtless highly com- 
plex genetically. If further analysis were possible, it might well turn 
out that dominance of the factors tending toward vigor in each respect 
is not even perfect. 
COAT COLOR. 
Six series of Mendelian factors are known which affect color in 
guinea pigs. Among our five leading inbred families there are 
variations in only two of these series, the albino series (C, c*, c4, ct, c*) 
and the agouti series (A, a’, a). All five families are piebald (s) 
instead of self (S), tortoise shell (e’) instead of self-black (KE) or self- 
red (e), black (B) instead of brown (b), and black (P) instead of 
pink-eyed pale sepia (p). 
TaBLE 11.—Color pattern and factorial composition of the five principal inbred families. 
oeth Factorial 
Family. | Color. composition. 
2. || Black-redswhitertricolomt. 25 26.5. os cies ae deceee Soe eee ee eee CCaa 
13 | Black-red-whitenicolores «<2. << = os sb aees « Sega mes Soden coon eee eee ace CCaa 
tvOccasional albimoseti ic 2 ses be oe ae ete ee Se eee cacaaa 
32... A gouti-red=wihitetricolore aint fede oc oso cles = Se caine eee ieee eee ee 
35: |. Yellow,agouti-yellow-white tricolor-.....0... jladeak ccc te. fleece eee eee ckckA A 
39 "A: couti-red-white tricolore..2 6.2 be ccae soo sae oe ce cee ce ee eee 
First crosses between Families 2 and 13 produce black-red-white 
tricolors. All other first crosses among these five families produce 
agouti-red-white tricolors, except that occasionally cream agouti- 
cream-white tricolors (ckc*Aa) appear in crosses between Families 
35 and 13. Segregation takes place in regular Mendelian fashion in 
later generations, there being no linkage between factors C and A. 
RESISTANCE TO TUBERCULOSIS. 
Experiments conducted cooperatively by the Bureau of Animal 
Industry and Dr. Paul A. Lewis, of the Henry Phipps Institute, have 
been described in another paper (Wright and Lewis, 1921). 
It was found that there was very little relation between age, weight, 
rate of gain, or sex, and the length of life after inoculation with 
tuberculosis. These factors combined determined less than 7 per 
cent of the variation in a very heterogeneous lot. 
